Three Universities, One Estimate, and a Gap Worth Closing
A working paper published on 24 September 2026 has put the first properly worked-through figure on the water side of Ireland's data centre industry. The authors are Seán Fearon, a research fellow at the Institute of Environmental Science and Technology at the Autonomous University of Barcelona, Patrick Bresnihan, associate professor in the School of Geography at Maynooth University, and Patrick Brodie, assistant professor in the School of Information and Communication Studies at University College Dublin. It appears as Working Paper 31 in the Maynooth University Social Sciences Institute series, under the title How we all pay for Big Tech.
Their central water estimate is this: the total water footprint associated with the electricity consumption of data centres in Ireland was approximately 125.9 million litres a day in 2025, giving an annual footprint of around 46 billion litres. Spread across roughly 85 active facilities, that averages 1.48 million litres a day per data centre. Taken cumulatively from 2015 to 2025, including both direct and indirect water use, the researchers put the sector's total footprint at an estimated 254.7 billion litres.
To make that legible, they convert it into households. Using CSO figures, they calculate that the sector's footprint was equivalent to the direct water consumption of 66,200 homes in 2015, 97,440 homes in 2018 and 175,800 homes by 2022. Applying an average Irish household consumption of 370 litres a day, the 2025 figure works out as equivalent to the direct water use of around 340,600 homes — about 18.5% of occupied dwellings in the State.
What the Number Actually Measures — and Why That Matters
It is worth being precise, because this figure is already being quoted loosely. This is not 46 billion litres pulled out of the public mains at the gates of Irish data halls. It is a footprint: the water embedded in generating the electricity those facilities consume, modelled using a water-intensity parameter from a United Nations University study of six litres per kilowatt hour, applied to CSO data on data centre electricity use.
That is a legitimate and widely used way of counting. Electricity is not water-free — thermal generation needs cooling, and every kilowatt hour carries a water cost somewhere upstream. But it measures something different from mains abstraction, and the paper says so plainly, noting that the household comparison sets total footprint consumption against direct household consumption only.
Holding both ideas at once is the mark of a serious reader. Direct mains use by Irish data centres is a much smaller number, historically put at roughly 0.13% of national supply. The footprint figure is far larger because it counts the water behind the power. Neither number is wrong. They answer different questions, and Ireland now has a credible published estimate for the second one for the first time.
The Finding Underneath the Finding
The most actionable line in the water chapter is not a litre count at all. The authors write that their estimates are based on publicly available data, and that research in this area would be substantially improved by the regular, detailed and transparent release of environmental data by tech companies resident in Ireland.
In other words: three academics across two countries had to model a national industry's water use from national electricity statistics and an international intensity parameter, because the facility-level figures that would have made modelling unnecessary are not published.
The paper is specific about the gap. The Irish data centre sector does not currently publish detailed power usage effectiveness or water usage effectiveness figures, the two standard efficiency metrics the industry already tracks internally for its own operations. It also notes that only 11 of Ireland's 82-plus data centres appear on the dedicated EU reporting database at the time of writing, under legislation that has already taken effect but carries no financial penalty for non-reporting.
Water Follows Electricity — Which Is Good News
Because the headline estimate is built on electricity consumption, it carries an implication that is easy to miss and genuinely encouraging: anything that reduces the water intensity of Irish electricity reduces the data centre water footprint automatically, with no action required at the facility itself.
The scale of the electricity side is set out in the same paper. Data centres in Ireland used 9.4TWh of electricity in 2025, around 23% of national grid demand. The water figure is a function of that consumption and of how the power behind it is generated. As Ireland continues to shift generation toward wind and solar — technologies with a very low water intensity compared with thermal plant — the embedded water cost of every kilowatt hour falls, and the footprint calculated in this paper falls with it.
The same logic applies to efficiency. A facility that improves its power usage effectiveness is not only cutting its electricity bill and its emissions; on this methodology, it is cutting its water footprint in exact proportion. For once, three separate sustainability objectives point in precisely the same direction, and the operational work that serves one serves all three.
For context on why researchers are paying attention at all, the United Nations University work the parameter comes from estimated the global water footprint linked to data centre electricity consumption at 4.5 trillion litres — a figure the authors compare to the annual basic water needs of 600 million people in Sub-Saharan Africa. Ireland's share of a global industry is being measured against a global yardstick, and doing well on that yardstick is a reasonable national ambition.
How Is It Actually Going Now?
The encouraging part is how small the remaining distance is. PUE and WUE are not new metrics that somebody has to invent. They are the numbers a data centre operations team looks at on a Monday morning. The operators already have them, already benchmark against them, and in many cases already report them to global parent companies for corporate sustainability disclosures filed in other jurisdictions.
The EU reporting framework exists and is live. The database exists. Eleven Irish facilities have already filed. The infrastructure for transparency, in other words, is built — what is missing is the habit of using it, and the operators who move first will be the ones who get to frame their own numbers rather than have them modelled for them.
There is a commercial argument here too, and it is the one most likely to move things. Uisce Éireann has been steadily improving its own picture of large industrial users. Planning authorities are asking harder questions at application stage. Corporate customers buying cloud capacity are increasingly required to report supply-chain resource use themselves. An operator with clean, published, year-on-year WUE figures is a far easier partner to work with in all three conversations than one whose water story has to be reconstructed by researchers from CSO tables.
What Good Looks Like From Here
Ireland is in an unusually strong position to lead on this, and that is not a consolation prize. It hosts one of the densest concentrations of hyperscale computing capacity in Europe, it has a national utility with a maturing view of large users, and it now has an academic literature putting real numbers on the table. Countries with all three at once are rare.
A practical path is visible. Annual facility-level publication of PUE and WUE, in a consistent format, filed to the EU database that already exists. Clear separation in public reporting between mains abstraction and total footprint, so the two figures stop being conflated. And continued investment in closed-loop and air-cooled designs, which several operators in Ireland have already adopted and which materially reduce direct water draw.
Every one of those steps is achievable inside a single reporting cycle. None of them requires new technology, and none of them requires an operator to disclose anything genuinely commercially sensitive. What they require is a decision.
The Bottom Line
The headline from Maynooth, UCD and Barcelona is 46 billion litres a year — but the finding that will actually change things is that the number had to be estimated at all. Ireland now has a defensible figure for the water footprint of its data centre electricity, and a clear account of exactly which disclosures would replace that estimate with something better. The metrics exist, the reporting database exists, and eleven facilities have already filed. Publishing the real numbers is the single cheapest sustainability improvement available to this sector, and the operators who do it first will be the ones setting the standard everybody else gets measured against.